Disposable plastic bags, particularly when made of thin polyethylene film having a wall thickness in the order of about 0.4 to about 2 mils, when overloaded, have a tendency to burst; if punctured, they also have a tendency to rip, the rip extending at random, and uncontrollably, and rapidly extending throughout the film of the bag. Puncture may occur for example by sharp object placed in the bag, cuttings of tin cans, nails, glass splinters or the like; even a comparatively small puncture which is small enough to prevent escape of the contents of the bag themselves may, when only slightly stressed (for example upon picking up of the bag) result in an uncontrollable and rapidly extending rip, resulting in spillage of the contents. Doubling the bag is no solution, and increasing the wall thickness of the bag rapidly increases the shipping weight of the material, and the costs. The costs for such bags should be kept as low as possible, and the amount of material to be used should be a minimum, consistent with the expected usage, in view of the fact that they are considered to be disposable and may be incinerated.
It is an object of the present invention to improve bags of this type by providing a reinforcement in the bag structure without, however, utilizing additional materials, or markedly increasing the cost of manufacture.
It is known that the strength of materials can be increased by forming ribs thereon; ribbed plastic material, as such, has been proposed previously and U.S. Pat. No. 2,750,631 sets forth, in general, a method of manufacturing ribbed sheet plastic. This patent is related, essentially, to an extrusion apparatus which is modified to provide sheet plastic material which has ribs thereon, essentially of square configuration.